1. Field of the Invention
The present invention relates to a semiconductor optical device, in particular, the invention relates to a semiconductor light-emitting device.
2. Related Background Art
A Japanese Patent Application published as JP-H05-082891A has disclosed a semiconductor laser diode (hereinafter denoted as LD) with a mesa structure that includes an n-type InGaAsP optical guiding layer, an un-doped InGaAsP active layer, a p-type InP cladding layer and a p-type InGaAsP contact layer. This LD further provides a semi-insulating iron-doped InP burying layer so as to bury the mesa structure in both sides thereof the structure to block the current flowing the burying layer, accordingly, to concentrate the current flowing in the mesa structure. Moreover, the LD provides another semi-insulating layer made of InGaAsP with the band gap energy smaller than that of InP, which is a material of the semiconductor substrate, so as to bury the semi-insulating InP burying layer.
Another Japanese Patent Application published as JP-2003-060310A has a semiconductor light-emitting device where the device has a structure to restrict the out diffusion of p-type dopants to the semi-insulating burying layer. This device includes a mesa structure with a stack of layers each formed on a semiconductor substrate. That is, the mesa structure includes a lower cladding layer with a first conduction type, an active region, and an upper cladding layer with a second conduction type. The device further provides semi-insulating semiconductor regions in both sides of the mesa structure, and this semi-insulating region includes a layer including dopants that accelerates the diffusion of impurities to make the upper cladding layer to be the second conduction type and another layer including other dopants that prevents the diffusion of the impurities. Two dopants in the semiconductor region make this region to be semi-insulating.
These semiconductor devices described above provide the configuration that a layer with high resistivity or a semi-insulating characteristic buries the mesa structure including the active layer and the contact layer. The contact layer of these devices, which is formed on the p-type cladding layer, is a p-type InGaAs or a p-type InGaAsP, and the p-type cladding layer, made of p-type InP, has a thickness of 1.5 μm.
Thinning the p-type cladding layer, which reduces the series resistance of the device, degrades the emission efficiency of the device. On the other hand, to make the p-type cladding layer thick to obtain desired emission efficiency increases the series resistance of the device.